Mercury,
May/June 2001 Table of Contents
Astronomers
have just identified a new class of white dwarf, which could number
in the hundreds of billions and account for a significant portion
of the galaxys dark matter.
by
Ben R. Oppenheimer
Ancient.
What images does that word suggest to you? Does it evoke visions
of Egypt, with its pyramids and long lost gods? Does it remind you
of Sumer, the first civilization? Or does it take you even further
back, perhaps to the earliest cave paintings? Maybe it brings up
images of Homo erectus or Triassic dinosaurs.
Compared
to a human lifespan, these events occurred an eternity ago. But
from an astronomical perspective, they occurred yesterday. To astronomers
like myself, "ancient" means near the beginning of time
itself. Fortunately, artifacts nearly as old as time exist, and
were starting to find them in our own solar neighborhood.
We are just beginning to study these artifacts, and were just
beginning to realize that there could be tens of billions or even
hundreds of billions in our galaxy, meaning they might outnumber
the normal stars in the galaxy.
These
artifacts are a breed of white dwarf, relics of our galaxys
first stars. They are the cores of stars, born perhaps as long as
13 billion years ago, when the universe just began to resemble its
present state, and our galaxy was no more structured than a lump
of mashed potatoes. These stars presumably went through the various
stages of stellar evolution in much the way that stars do today,
eventually leaving behind white dwarfs, extremely dense spheres
of carbon and oxygen with traces of hydrogen and helium.
Understanding
these ancient white dwarfs, their temperatures, and how numerous
they are, will ultimately reveal the age of the galaxy. Even more
exciting is that the discovery of vast numbers of old white dwarfs
challenges our conception of star formation, and may represent the
first time astronomers have actually seen the so-called "dark
matter."
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